The present invention relates to a rotation angle measuring apparatus for measuring the rotation angle from any given reference rotation position of a rotatory body which makes a rotational motion in a forward/reverse direction.
The conventional rotation angle measuring apparatus is constructed such that a phase difference between two signals phase-shifted from each other by 90.degree. is determined to discriminate the direction of rotation of a rotatory body, as has been disclosed by, for example, JP-A-No. 56-2709. However, in the case where the rotatory body makes a reciprocating motion in a certain range of rotation angle while repeatedly changing the direction of rotation, the measurement of the rotation angle involves an error.
Explanation will first be made of the case where two phase signals are doubled in frequency. FIG. 1 shows a circuit diagram of one example of the conventional rotation angle measuring apparatus in which the direction of rotation is determined from two signals phase-shifted from each other by 90.degree.. Referring to FIG. 1, reference numeral 1 designates an A-phase input terminal, numeral 2 a B-phase input terminal, numeral 5 a D flip-flop, numeral 6 an up/down counter, and numeral 22 an exclusive OR gate. A-phase and B-phase signals 1a and 2a are supplied from the A-phase and B-phase input terminals 1 and 2, respectively. The A-phase signal 1a is applied to one input of the exclusive OR gate 22 and a data input terminal 5a of the D flip-flop 5 while the B-phase signal 2a is applied to the other input of the exclusive OR gate 5 and a clock input terminal 5b of the D flip-flop 5. A signal of an output 22a of the exclusive or gate 22 (or a signal of exclusive OR operation of the A-phase and B-phase signals 1a and 2a) is applied to a clock input terminal 6a of the up/down counter 6 while a signal of a Q-output 5c of the D flip-flop 5 (or a direction signal) is applied to an up/down change-over input terminal 6b of the up/down counter 6.
FIG. 2 is a time chart which illustrates the operation of the circuit shown in FIG. 1. For example, now assume the case where a rotatory body (not shown) which has rotated in a forward direction makes in a repeating period of time between instants 101 and 102 a reciprocating motion in which the direction of rotation changes from the forward direction to a reverse direction and vice versa. Then, since the circuit shown in FIG. 1 is designed such that the A-phase signal 1a is taken in the D flip-flop 5 as data at only the time of rise of the B-phase signal 2a, the direction signal 5c entering the up/down change-over input terminal 6b of the up/down counter 6 does not change as it has indicated the forward direction of rotation. Namely, notwithstanding that the actual rotation angle repeats a reciprocative span in the repeating period of time between instants 101 and 102, the up/down counter 6 continues its count-up operation since the direction signal (or direction discrimination signal) 5c has no change with the "1" level to which it is turned by the rise of the B-phase signal 2a at instant of time 201. As a result, an error takes place in the measurement of the rotation angle.
Next explanation will be made of the case where two phase signals are not doubled in frequency. FIG. 3 shows a circuit diagram of another example of the conventional rotation angle measuring apparatus in which the direction discrimination and the counting are effected by the rise of one of two phase signals. Through the figures of the accompanying drawings, the same reference numerals or symbols are used for designating the identical or corresponding components. An A-phase signal 1a on an A-phase input terminal 1 is applied to a data input terminal 5a of a D flip-flop 5 while a B-phase signal 2a on a B-phase input terminal 2 is applied to a clock input terminal 5b of the D flip-flop 5 and a clock input terminal 6a of an up/down counter 6. A signal of a Q-output 5c of the D flip-flop 5 is applied to an up/down change-over input terminal 6b of the up/down counter 6.
FIG. 4 is a time chart which illustrates the operation of the circuit shown in FIG. 3. Now consider the case where a rotatory body rotates in a forward direction. At instant of time 201 shown by arrow in FIG. 4, the A-phase signal 1a applied to the data input terminal 5a of the D flip-flop 5 takes the level of "1". When the B-phase signal 2a applied to the clock input signal 5b of the D flip-flop 5 rises at this instant of time 201, a signal of "1" (direction signal) is supplied from the Q-output 5c of the D flip-flop 5 to the up/down change-over input terminal 6b of the up/down counter 6 so that the up/down counter 6 takes a count-up condition. At the same time, the B-phase signal 2a branching from the B-phase input terminal 2 is supplied to the clock input terminal 6a of the up/down counter 6 so that the counting by the counter 6 in a forward direction is effected by the rise of the pulse of the B-phase signal 2a. Next consider the case where the rotatory body rotates in a reverse direction. Then, the B-phase signal 2a rises at instant of time 202 indicated by arrow. Since the A-phase signal 1a is in the level of "0" at that time, a signal of "0" (direction signal) is supplied from the Q-output 5c' of the D flip-flop 5 to the up/down change-over input terminal 6b of the up/down counter 6 so that the counting by the counter 6 in a reverse direction is effected by the rise of the B-phase signal 2a applied to the clock terminal 6a of the counter 6.
In the just-mentioned type of apparatus, since the direction discrimination and the counting are effected by only the rise of the B-phase signal 2a, there is no problem if the counting is made after the direction discrimination has been made. However, in the case where the counting is made before the direction discrimination, an error may be produced, thereby making the measurement inaccurate.
FIG. 5 shows a circuit diagram of a further example of the conventional rotation angle measuring apparatus in which the direction discrimination is effects by the rise of one of two phase signals and thereafter the counting is effected by the rise of the other phase signal. In FIG. 5, reference numeral 23 designates an inverter. The construction of the circuit shown in FIG. 5 is different from the circuit of FIG. 3 in that an A-phase signal 1a is used as an input signal to a clock input terminal 6a of an up/down counter 6. Practically, the A-phase signal 1a is inverted by the inverter 23 and an A-phase signal on the inverted output 23a of the inverter 23 is used as the clock input signal to the clock input terminal 6a of the up/down counter 6.
FIG. 6 is a time chart which illustrates the operation of the circuit shown in FIG. 5. In the case where a rotatory body rotates in a forward direction, the A-phase signal 1a applied from the A-phase input terminal 1 to a data input terminal 5a of a D flip-flop 5 is in the level of "1" at instant of time 201 indicated by arrow. By the rise 201 of the pulse of the B-phase signal 2a applied to the clock input terminal 5b of the D flip-flop 5 at this time a signal of "1" of a Q-output 5c of the D flip-flop 5 (direction signal) is delivered to an up/down change-over input terminal 6b of the up/down counter 6 so that the counter 6 takes a count-up condition. Thereafter, at instant of time 231 indicated by arrow, the rise 231 of the A-phase signal on the output 23a of the inverter 23 applied to the clock terminal 6a of the up/down counter 6 causes the counter to perform its counting operation. On the other hand, in the case where the rotatory body rotates in a reverse direction, the A-phase signal 1a is in the level of "0" at instant of time 202 indicated by arrow and at this time the rise 202 of the pulse of the B-phase signal 2a causes the direction signal of "0" on the Q-output 5c' of the D flip-flop 5 to be inputted to the up/down change-over input terminal 6a of the up/down counter 6. Thereafter, at instant of time 232 indicated by arrow, the rise 232 of the A-phase signal effects a counting operation of the counter 6 in a reverse direction or a count-down operation.
In the circuit shown in FIG. 5, in the case where the rotatory body makes a reciprocating motion in a repeating period of time between instants 101 and 102 indicated by dotted chain lines, the B-phase signal 2a only repeats its rise 201 at instant of time 201 indicated by arrow. Since the A-phase signal 1a is always in the level of "0" at that time, the direction signal on the Q-output 5c of the D flip-flop 5 is not changed or is always maintained to the level of "1". Accordingly, the up/down counter 6 repeats the counting operation in the forward direction or the count-up operation, thereby causing a measurement error.
JP-A-No. 61-198018 discloses a position detecting apparatus including means by which each time a rotating signal of a rotatory body changes, the forward/reverse direction rotation direction of the signal immediately after the change is discriminated. However, the discriminating means requires three sensors, which makes the circuit construction complicate.
As is apparent from the foregoing, though the above-described conventional rotation angle measuring apparatuses discriminate the rotation direction of a rotatory body on the basis of two phase signals having a phase difference therebetween, no consideration is taken of the case where the rotatory body makes a reciprocating motion while repeatedly changing the rotation direction in a certain range of rotation angle. Therefore, there is a problem that the measurement of the rotation angle involves an error.